1. Field of the Invention
The present invention relates generally to light guide devices, and more particularly, to a light guide apparatus applied to a direct type backlight module.
2. Description of the Related Art
Several years ago, large-scale liquid crystal display (LCD) is mostly applied to a laptop computer or an LCD monitor or the like. However the LCD does not emit light itself, thereby an external light source is needed for illumination and image displaying. The backlight module applied thereto is preferred to be light in weight, small in size and thin in thickness. In recent years, when the backlight module is applied to a large panel, such as LCD TV, it is required that the backlight module has properties like high display luminance, broad visual angle, distinct image contrast and long life. Therefore, direct type backlight module, which takes the place of lateral light source applied to prior arts for lightening the weight and thickness thereof, evenly scatters the lights, coverts the lights into area lights, and guides the lights into the LCD panel, thereby meeting the requirements mentioned above.
LCD monitor, thin film transistor (TFT) in particular, generally applies backlight module as light source. The lights of the backlight module are generated by cold cathode fluorescernt lamp (CCFL) or light emitting diode (LED). The CCFL has properties like high brightness, high efficiency, long life and high color rendering index, and additionally has a cylinder-shaped configuration which is easily coupled with light reflecting components to form laminal lighting device. Consequently, the CCFL is widely used in flat panel display (FPD).
In the direct type backlight module, the CCFLs are usually aligned in a row and disposed at a bottom of the LCD panel. Such arrangement creates the problem that the profiles of the CCFLs unevenly distribute luminance, and cast shadows on the screen of the LCD. That is, for meeting the demand of high luminance, conventional direct type backlight module applied great number of the CCFLs thereto, as a result, with the increasing of the number of the CCFLs, the deficiency of black and white strips of shadows shown on the screen of the LCD becomes more serious.
To solve the aforementioned problem, U.S. Pat. No. 5,253,151 provides a solution titled as “luminaire for use in backlighting a liquid display matrix”. Referring to FIG. 1, the luminaire 10 comprises at least one light generating unit 11 and a reflector. The reflector 12 has a special shaped structure which can guide the lights of the light generating unit 11 to an LCD module, and reflect the lights of the light generating unit 11 rearwardly scattered, thereby making full use of the lights of the light generating unit 11.
However, this special shaped structure of the reflector 12 is so complicated that elaborate and time consuming calculation and design must be preprocessed. Thus problems like difficulty of manufacture, rising of costs and inconvenience of assembly are presents.
U.S. Pat. No. 6,407,781 discloses another LCD device titled “LCD device having electronic formed within concave portion of a reflector”. Referring to FIG. 2, the LCD device 20 includes an LCD panel 21 and a resin frame member 22 having a reflecting plate 23. The resin frame member 22 is disposed at a backside of the LCD panel 21. The reflecting plate 23 comprises a wavy structure designed for reflecting the lights emitted by light sources 24.
However, the LCD device 20 merely serves as a light reflector, and can not thoroughly solve the problem of energy waste under the circumstance of the reflected lights enter into the light source again. Furthermore, the LCD device 20 can not perform a guiding function for the reflected lights, that is, can not adjust the distribution of the reflected lights to achieve greater light utilization efficiency.
Additionally, the problems, such as the luminance quality and the replacing of the CCFLs when the CCFLs fail in a direct type of backlight module, are still unsolved in the conventional devices. Accordingly, obvious low luminance area and uneven light distributing caused by the above problems, and severely affect the service life of the direct type backlight module products.
Moreover, conventional direct type backlight module is composed of a plurality of CCFLs and a reflecting plate for reflecting the lights emitted from the bottom of the CCFLs toward the LCD panel. However, the conventional reflecting plate does not have the function of adjusting the travel passages of the reflected lights, thereby part of the lights are reflected back into the CCFLs and wasted. Thus the light utilization efficiency of the CCFLs is decreased.